1. Field of the Invention
The present invention relates to a device for efficiently embedding a digital watermark in a picture and a control method of the device, and to a device for extracting the digital watermark from the picture data and a control method of the device.
2. Description of the Related Art
Recently, because of the rapid development and spread of computers and networks, various types of information such as text data, picture data, voice data, etc. is being digitized. Digital information does not deteriorate over time and can be permanently stored in a perfect state, however it can be easily reproduced by a third party and accordingly copyright protection has become a major issue. In such a context, the importance of security technologies for protecting copyright has rapidly increased.
Digital watermark technology is known as one technology for protecting copyrights. Digital watermarking is a technology to embed information such as the name of the copyright holder or an ID of a purchaser, etc. in digitized picture data, voice data, text data, etc. in such a manner as to prevent a person from recognizing them and to pursue usage of the content without permission by illegal reproduction.
Conventionally, as a methodology to embed a digital watermark, a method using pseudo-random number sequences is known. For example, in a technique for embedding any one of plural kinds of added information, respective pseudo-random number sequences in one-to-one correspondence with each kind of added information are prepared, and the picture data is modulated using the pseudo-random number sequence corresponding with one kind of added information desired to be embedded, thereby embedding the added information.
In this technique, the added information can be extracted from the picture data in which it is embedded by using the pseudo-random number sequence corresponding to that used when embedding and by performing a convolution operation.
However, in the related art described above, normally only one kind of added information is embedded by using any one of the pseudo-random number sequences for one picture, and a technology for increasing the quantity of embeddable added information has not yet been developed.